U.S. patent number 5,972,811 [Application Number 09/090,789] was granted by the patent office on 1999-10-26 for polybutadiene and polyisoprene thermosetting compositions and method of manufacture thereof.
This patent grant is currently assigned to World Properties, Inc.. Invention is credited to Samuel Gazit, Doris I. Hand, Vincent R. Landi, Raymond R. Miskiavitch, Michael E. St. Lawrence, Robert H. Walker.
United States Patent |
5,972,811 |
St. Lawrence , et
al. |
October 26, 1999 |
Polybutadiene and polyisoprene thermosetting compositions and
method of manufacture thereof
Abstract
An electrical substrate material is presented comprising a
thermosetting matrix of polybutadiene or polyisoprene and a
co-curable second resin distinct from the first resin. A peroxide
cure initiator and/or crosslinking agent may optionally be added.
The presence of a very high surface area particulate filler,
preferably fumed silica, is also preferred, in that its presence
results in a prepreg which has very little tackiness and can
therefore be easily handled by operators. This low tackiness
feature allows for the use of conventional automated layup
processing, including foil cladding, using one or more known roll
laminators. While the prepreg of this invention is tack-free enough
to be handled relatively easily by hand, it is also tacky enough to
be tacked to itself using a roll laminator (e.g., nip roller) at
room temperature. The composition of this invention is particularly
well suited for making electrical circuit substrates for microwave
and digital circuits, typically in the form of the thermosetting
composition being laminated onto one or both opposed surfaces to a
metal conductive foil such as copper.
Inventors: |
St. Lawrence; Michael E.
(Thompson, CT), Hand; Doris I. (Dayville, CT), Landi;
Vincent R. (Danielson, CT), Walker; Robert H. (Phoenix,
AZ), Gazit; Samuel (Bet Lechem HaGlilit, IL),
Miskiavitch; Raymond R. (Putnam, CT) |
Assignee: |
World Properties, Inc.
(Lincolnwood, IL)
|
Family
ID: |
24774531 |
Appl.
No.: |
09/090,789 |
Filed: |
June 4, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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690929 |
Aug 1, 1996 |
5858887 |
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322890 |
Oct 13, 1994 |
5571609 |
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Current U.S.
Class: |
442/237; 442/173;
442/180; 524/571; 442/234; 442/233 |
Current CPC
Class: |
C08J
5/24 (20130101); C08K 3/22 (20130101); C08K
3/34 (20130101); C08K 3/40 (20130101); C08K
5/0066 (20130101); C08K 7/14 (20130101); C08L
9/00 (20130101); H05K 1/032 (20130101); H05K
1/0366 (20130101); H05K 1/0373 (20130101); C08K
3/22 (20130101); C08L 9/00 (20130101); C08K
3/34 (20130101); C08L 9/00 (20130101); C08K
3/40 (20130101); C08L 9/00 (20130101); C08K
5/0066 (20130101); C08L 9/00 (20130101); C08K
7/14 (20130101); C08L 9/00 (20130101); C08L
9/00 (20130101); C08L 9/00 (20130101); C08L
9/00 (20130101); Y10T 442/2934 (20150401); C08L
7/00 (20130101); C08L 9/02 (20130101); C08L
9/06 (20130101); C08L 15/00 (20130101); C08L
23/04 (20130101); C08L 53/00 (20130101); H05K
1/0203 (20130101); H05K 1/162 (20130101); H05K
2201/012 (20130101); H05K 2201/0133 (20130101); H05K
2201/0158 (20130101); H05K 2201/0209 (20130101); H05K
2201/0212 (20130101); H05K 2201/0251 (20130101); H05K
2201/0278 (20130101); H05K 2201/029 (20130101); H05K
2201/0293 (20130101); C08J 2309/00 (20130101); Y10T
442/3431 (20150401); Y10T 442/3455 (20150401); Y10T
442/3423 (20150401); Y10T 442/2992 (20150401); C08L
2666/06 (20130101); C08L 2666/08 (20130101); C08L
2666/24 (20130101) |
Current International
Class: |
C08J
5/24 (20060101); H05K 1/03 (20060101); H05K
1/02 (20060101); H05K 1/16 (20060101); B32B
007/00 () |
Field of
Search: |
;442/173,180,233,234,237
;524/571 |
References Cited
[Referenced By]
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EP |
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0707038A1 |
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253412 |
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26 48 595 |
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JP |
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050309651 |
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JP |
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1195567 |
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Jun 1970 |
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GB |
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2 172 892 |
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Oct 1986 |
|
GB |
|
Other References
"High Vinyl 1-2 Liquid Polybutadiene-Ricon Molding Compounds
CCS-110" Feb. 1, 1980 Colorado Chemical Spec. .
Colorado Chemical Brochure--"Ricon Product Bulletin", Aug. 20, 1985
High Vinyl 1-2 Liquid Polybutadiene. .
Colorado Chemical Brochure--"Ricon Radome" High Vinyl 1-02 Liquid
Polybutadiene. .
N. Sawatari, I. Watanabe, H. Okuyama and K. Murakawa, "A New Flame
Retardant, 1,2-Polybutadiene Laminate", 1983 pp. 131-137. .
C.F. Chen, "Dielectric Properties Of Polybutadiene And its
Reinforced Composites At Room And Elevated Temperature" pp.
318-320. .
Ronald E. Drake, "1,2-Polybutadienes-High Performance Resins For
The Electrical Industry", pp. 730-733. .
Bruzzone et al., LaChimica E. L'Industria 47 (12) 1298-1302 (1965)
"High-Temperature Thermal Cross-Linking of Cistatic Polybutadiene".
.
Nippon Soda Brochure- "Nisso-PB". .
McCreedy et al., Polymer 20(4)(1979) "Effect of Thermal
Crosslinking on Decomposition of Polybutadiene". .
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1,2-polybutadiene," in New Industrial Polymers, ACS #4, pp. 15-25.
.
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Barth et al., Modern Plastics pp. 142-148, *(Nov. 1970)
"Fast-Curing Polybutadiene Thermosetting Resins"..
|
Primary Examiner: Pezzuto; Helen L.
Attorney, Agent or Firm: Cantor Colburn LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation of application Ser. No.
08/690,929, filed on Aug. 1, 1996, now U.S. Pat. No. 5,858,887,
which is a continuation-in-part of application Ser. No. 08/322,890,
filed on Oct. 13, 1994, now U.S. Pat. No. 5,571,609.
Claims
What is claimed is:
1. A laminate for making an electrical circuit comprising:
(1) a substrate material having two opposed surfaces and
including:
(a) a thermosetting composition consisting essentially of a
polybutadiene or polyisoprene resin and at least one unsaturated
polymer capable of participating in crosslinking with the
polybutadiene or polyisoprene resin, the polybutadiene and
polyisoprene resin being chemically distinct from the at least one
polymer;
(b) a woven fabric in an amount greater than about 10 percent of
the substrate material; and
(c) a particulate filler in an amount greater than about 5 volume
percent of the substrate material; and
(2) a conductive material laminated to at least a portion of at
least one of the opposed surfaces of said substrate material,
at least said thermosetting composition and said particulate filler
having been formed into a prepreg sheet prior to being laminated,
and wherein curing of said substrate material occurs when said
conductive material is laminated under heat and pressure to said
substrate.
2. The substrate material of claim 1, wherein:
the unsaturated polymer is a solid thermoplastic elastomer block
copolymer.
3. The substrate material of claim 1 wherein:
the particulate filler is present in an amount by volume which is
greater than the amount by volume of the woven fabric.
4. The substrate material of claim 1 wherein:
the particulate filler is present in an amount by volume which is
greater than the amount by volume of the thermosetting
composition.
5. The substrate material of claim 1 wherein:
the particulate filler comprises a high surface area particulate
filler in an amount of from about 0.2 volume percent to about 5
volume percent.
6. The substrate material of claim 1 wherein:
the high surface area particulate filler is fumed silica.
7. The substrate material of claim 1 wherein:
the particulate filler comprises a dielectric material selected
from the group consisting of titanium dioxide, barium titanate,
strontium titanate, silica, fused amorphous silica, fumed silica,
corundum, wollastonite, polytetrafluoroethylene, aramide fibers,
fiberglass, Ba.sub.2 Ti.sub.9 O.sub.20, glass spheres, quartz,
boron nitride, aluminum nitride, silicon carbide, beryllia, alumina
and magnesia.
8. The substrate material of claim 1, wherein:
the particulate filler is present in an amount of between about 30
and 50 volume percent of the substrate material.
9. The substrate material of claim 1, wherein:
the woven fabric is present in amount of between about 15 and 25
volume percent of the substrate material.
10. The substrate material of claim 1 wherein:
said conductive material is a metal layer having a preselected
coefficient of thermal expansion, wherein the filler and the
quantity thereof provide to the electrical substrate material a
coefficient of thermal expansion substantially equal to that of the
metal layer.
11. The substrate material of claim 1 further including:
a free radical cure initiator, a flame retardant, a cross-linking
agent, or a combination thereof.
12. The substrate material of claim 2, wherein
the thermoplastic elastomer is a linear block copolymer or
graft-type block copolymer having at least one thermoplastic
block.
13. The substrate material of claim 2, wherein
the at least one thermoplastic block is a styrene block or an
.alpha.-methyl styrene block.
14. The substrate material of claim 1, wherein
the thermosetting composition further comprises a free radical
co-curable polymer which is chemically distinct from the
polybutadiene or polyisoprene resin and the at least one
unsaturated polymer, wherein the co-curable polymer comprises less
than 50 volume % of the thermosetting composition, and wherein the
co-curable polymer is selected from the group consisting of
primarily 1,3-addition butadiene-styrene copolymers, primarily
1,3-addition isoprene-styrene copolymers, primarily 1,3-addition
butadiene-.alpha.-methyl styrene copolymers, primarily 1,3-addition
isoprene-.alpha.-methyl styrene copolymers, primarily 1,3-addition
butadiene-acrylate copolymers, primarily 1,3-addition
isoprene-acrylate copolymers, primarily 1,3-addition
butadiene-methacrylate copolymers, primarily 1,3-addition
isoprene-methacrylate copolymers, primarily 1,3-addition
butadiene-acrylonitrile copolymers, primarily 1,3-addition
isoprene-acrylonitrile copolymers, polyethylene, ethylene
copolymers, ethylene-propylene copolymers, ethylene-propylene-diene
terpolymers, ethylene-ethylene oxide copolymers, natural rubber,
norbornene polymers, polydicyclopentadiene; hydrogenated diene
polymers, hydrogenated styrene-isoprene-styrene copolymers, and
hydrogenated butadiene-acrylonitrile copolymers.
15. The laminate of claim 1, wherein:
said conductive material is a layer of conductive metal.
16. The laminate of claim 1, wherein:
said conductive material is a layer of copper.
17. The laminate of claim 1, further including:
said conductive material being laminated to a least a portion of
each of said second opposing surface.
18. The laminate of claim 17, wherein:
said conductive material is copper.
19. The laminate of claim 1, wherein:
said prepreg further includes said woven fabric.
20. The laminate of claim 1, wherein:
said woven fabric is present in an amount from about 10 to about 40
volume percent with respect to the substrate, and said particulate
filler is present in an amount of from about 5 to about 60 volume
percent with respect to the substrate.
21. The laminate of claim 1, wherein:
said thermosetting composition is present in an amount of from
about 25 to about 50 volume percent with respect to the
substrate.
22. The laminate of claim 1, wherein:
said polybutadiene or polyisoprene resin has pendant vinyl groups
for crosslinking, and said at least one polymer has pendant vinyl
groups for cross-linking with the polybutadiene or polyisoprene
resin.
23. The laminate of claim 1, wherein:
said at least one unsaturated polymer is a thermoplastic
elastomer.
24. The laminate as in claims 14, 20, 21, or 22 wherein:
said unsaturated polymer is a thermoplastic elastomer.
25. The laminate as in 24, wherein:
said at least one unsaturated polymer is a solid thermoplastic
elastomer block copolymer.
26. The laminate as in claims 14, 20, 21, or 23, wherein:
said at least one unsaturated polymer is a linear block copolymer
or graft-type block copolymer having at least one thermoplastic
block.
27. The laminate as in claim 26, wherein:
said at least one thermoplastic block is a styrene block or an
.alpha.-methyl styrene block.
28. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said particulate filler is present in an amount by volume which is
greater than the amount by volume of the woven fabric.
29. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said particulate filler is present in an amount by volume which is
greater than the amount by volume of the thermosetting
composition.
30. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
the particulate filler comprises a high surface area particulate
filler in an amount of from about 0.2 volume percent to about 5
volume percent.
31. The laminate as in 30, wherein:
the high surface area particulate filler is fumed silica.
32. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
the particulate filler comprises a dielectric material selected
from the group consisting of titanium dioxide, barium titanate,
strontium titanate, silica, fused amorphous silica, fumed silica,
corundum, wollastonite, polytetrafluoroethylene, aramide fibers,
fiberglass, Ba.sub.2 Ti.sub.9 O.sub.20, glass spheres, quartz,
boron nitride, aluminum nitride, silicon carbide, beryllia, alumina
and magnesia.
33. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
the particulate filler is present in an amount of between about 30
and 50 volume percent based on the total substrate.
34. The laminate as in claim 33, wherein:
the woven fabric is present in an amount of between about 15 and 25
volume percent based on the total substrate.
35. The laminate as in claims 14, 20, 21, 22 or 23, wherein:
the woven fabric is present in an amount of between about 15 and 25
volume percent based on the total substrate.
36. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said thermosetting composition further comprises a free radical
cure initiator, a flame retardant, a cross-linking agent, or a
combination thereof.
37. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said conductive material is a layer of metal having a preselected
coefficient of thermal expansion, wherein the filler and the
quantity thereof provide to the electrical substrate material a
coefficient of thermal expansion substantially equal to that of the
metal layer.
38. The laminate as in claims 14, 20, 21, 22, or 23, wherein: said
conductive material is a layer of conductive metal.
39. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said conductive material is a layer of copper.
40. The laminate as in claims 14,20,21,22, or 23, further
including:
said conductive material being, laminated to a least a portion of
each of said two opposing surfaces.
41. The laminate of claim 40, wherein:
said conductive material is copper.
42. The laminate as in claims 14, 20, 21, 22, or 23, wherein:
said prepreg further includes said woven fabric.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a method of making
thermosetting composites and the resulting product which preferably
comprises electrical circuit laminate materials. More particularly,
this invention relates to an electrical circuit laminate comprising
(1) a thermosetting resin of polybutadiene or polyisoprene; (2) a
woven fibrous web impregnated with the resin; and (3) inorganic
particulate filler such as silica, titania and the like. In
accordance with an important feature of this invention, the filler
loadings for both the woven web (fabric) and particulate filler are
selected such that individual layers are relatively tack free
thereby allowing ease of handling for lamination without the need
for B-staging. The material of this invention allows for relatively
low lamination temperatures.
Commonly assigned U.S. Pat. No. 5,223,568 (which is fully
incorporated herein by reference) describes a thermosetting
composition which is particularly useful for making electrical
substrate materials. In general, U.S. Pat. No. 5,223,568 describes
a composition formed from the steps of:
(a) providing a moldable thermosetting composition that includes
(1) polybutadiene or polyisoprene resin which is a liquid at room
temperature and which has a molecular weight less than 5,000 and
(2) a solid butadiene or isoprene-containing polymer capable of
cross-linking with the polybutadiene or polyisoprene resin;
(b) forming the composition into a shape; and
(c) curing the composition to produce the electrical substrate
material including subjecting the composition to a high temperature
cure condition at a temperature greater than about 250.degree. C.
and less than the decomposition temperature of the composition.
This composition thus comprises a two component system, the first
component being the polybutadiene or polyisoprene resin and the
second component being the solid butadiene or isoprene-containing
polymer, all of which are subjected to the high temperature curing
cycle (e.g., greater than 250.degree. C.).
In preferred embodiments, the solid polymer is a thermoplastic
elastomer block copolymer.
U.S. Pat. No. 5,223,568 also describes a composition with a
dielectric filler (i.e., a material having a dielectric constant
greater than about 1.2 at microwave frequencies) homogeneously
dispersed throughout the composition to the extent that when the
composition is cured the properties of the cured article, e.g.,
dielectric constant and coefficient of thermal expansion, do not
vary more than about 5% throughout the article.
In preferred embodiments, the composition of U.S. Pat. No.
5,223,568 further includes a crosslinking agent capable of
co-curing (i.e., forming covalent bonds) with the polybutadiene or
polyisoprene resin thermoplastic elastomer, or both. Examples of
preferred crosslinking agents include triallylcyanurate,
diallylphthlate, divinyl benzene, a multifunctional acrylate, or
combinations of these agents.
When the electrical substrate material disclosed in U.S. Pat. No.
5,223,568 includes a dielectric filler, the volume % of the filler
(based upon the combined volume of resin, thermoplastic elastomer,
crosslinking agent, if any, and filler) is between 5 and 80%,
inclusive. Examples of preferred fillers include titanium dioxide
(rutile and anatase), barium titanate, strontium titanate, silica
(particles and hollow spheres); corundum, wollastonite,
polytetrafluoroethylene, aramide fibers (e.g., Kevlar), fiberglass,
Ba.sub.2 Ti.sub.9 O.sub.20, glass spheres, quartz, boron nitride,
aluminum nitride, silicon carbide, beryllia, or magnesia. They may
be used alone or in combination.
The method disclosed in U.S. Pat. No. 5,223,568 provides a wide
variety of shaped articles having favorable isotropic thermal and
dielectric properties. These properties can be tailored to match or
complement those of ceramic materials, including gallium arsenide,
alumina, and silica. Thus, the cured articles can replace ceramic
materials in many electronic and microwave applications, for
example, as specialized substrates for high speed digital and
microwave circuits. Examples of microwave circuits include
microstrip circuits, microstrip antennas, and stripline circuits.
The cured products are also useful as rod antennas and chip
carriers.
While well suited for its intended purposes, the circuit laminate
materials described in U.S. Pat. No. 5,223,568 do suffer from
several drawbacks. For example, these prior art materials require a
high temperature cure (e.g., lamination) of greater than about
250.degree. C. (482.degree. F.); and this requirement is
problematic for several reasons. First, conventional circuit
fabrication equipment often exhibit temperature limits of
360.degree. F. (182.degree. C.), which is below that of the
482.degree. F. (250.degree. C.) requirement. Still another drawback
is that flammability ratings required by Underwriters Laboratory UL
94-VO lead to the need for inclusion of a flame retardant additive
such as a bromine-containing fire retardant. Unfortunately, typical
bromine-containing fire retardant additives cannot withstand the
high temperature cure conditions of greater than 250.degree. C.,
undergoing decomposition and/or chemical degradation at these
temperatures.
In addition to the foregoing need for lowering the cure
(lamination) temperature of the circuit laminates, there is also a
problem with the inherent tackiness associated with the
polybutadiene or polyisoprene laminate prepregs. Because of the
tacky nature of the prepreg, it is not practically feasible to use
a continuous, automated layup process for laminating circuit
materials. Roll lamination equipment is commonly available,
however, and the ability to provide a polybutadiene or polyisoprene
based prepreg of the type described in U.S. Pat. No. 5,223,568
which is also usable in an automatic layup process would greatly
reduce the manufacturing cost and processing time, leading to a
significant increase in the commercial success of the resultant
circuit material products.
In addition to U.S. Pat. No. 5,223,568, there are other prior art
patents and literature of some interest which respect to the use of
filled circuit laminates in general, and polybutadiene based
circuit laminates in particular. For example, in an article
entitled "A New Flame Retardant 1,2-Polybutadiene Laminate" by N.
Sawatari et al., IEEE Transactions on Electrical Insulation, Vol.
EI-18, No. 2, Apr. 1983, the limitations on presently-used
polybutadiene based laminates is discussed, including the fact that
1,2-polybutadiene (PBD) is difficult to control in the semicured
condition (the B-stage), difficult to make non-tacky, highly
flammable, and exhibits low copper bond. The article thereafter
describes a composition which addresses these issues. The
composition described uses a high percentage of very high molecular
weight PBD to eliminate tackiness and B-staging. Also, a low
molecular weight, modified PBD resin is used as a minor component
to aid in copper bond and flow during lamination. There is no
mention of using filler of any type.
U.S. Pat. No. 5,264,065 to Kohm describes a base material for
printed wiring boards where inert filler is used to control Z-axis
coefficient of thermal expansion (CTE) in fiberglass-reinforced
thermoset resins. The Kohm patent discloses a range of 45-65 weight
% fiberglass reinforcement and a range of 30 to 100 parts filler
per 100 parts of the polymer. There is no disclosure in Kohm of a
polybutadiene or like material for the resin system.
U.S. Pat. No. 4,997,702 to Gazit et al. discloses a circuit
laminate having an epoxy resin system which also includes inorganic
fillers or fibers in the range of 20-70 weight % of the total
composite. The fibers include both glass and polymeric fibers and
the fillers include clay or mineral (e.g. silica) particulate
fillers.
U.S. Pat. No. 4,241,132 to Pratt et al. discloses an insulating
board comprising a polymeric matrix such as polybutadiene and a
filler consisting of polymeric filler, for example fibrous
polypropylene. In all cases, the dielectric constant or dissipation
factor of the resin matrix is matched to the fibrous reinforcement
in order to obtain an isotropic composite.
European Patent No. 0 202 488 A2 discloses a polybutadiene-based
laminate wherein a high molecular weight, bromine-containing
prepolymer is used to reduce tack and flammability of a
1,2-polybutadiene resin. Similarly, in Japanese Patent No.
04,258,658, a high molecular weight compound is added to a tacky
PBD resin to control tack. The compound utilized is a
halogen-containing bismaleimide which provides flammability
resistance, as well as good copper bonding and heat resistance.
There is no mention of the use of fillers and the resulting
laminate will have a relatively high dissipation factor.
An article entitled "1,2-Polybutadienes-High Performance Resins for
the Electrical Industry", by R. E. Drake, ANTEC '84 pp. 730-733
(1984), generally discloses conventional polybutadiene resins for
use in laminates and specifically discloses the use of reactive
monomers to co-cure with the PBD.
U.K. Patent Application No. 2 172 892 A generally discloses
laminates composed of styrene-containing and thermoplastic
copolymers with unsaturated double bonds and polybutadiene.
Notwithstanding the foregoing examples of laminate composites,
there continues to be a need for improved polybutadiene laminates
having a combination of electrical, chemical, mechanical and
thermal properties which are not presently available including
flame retardance, improved CTE, ability to tailor dielectric
constant, improved dissipation factor, low cost and low
tackiness.
SUMMARY OF THE INVENTION
The above-discussed and other drawbacks and deficiencies of the
prior art are overcome or alleviated by the electrical substrate
material of the present invention. In accordance with one
embodiment of the present invention, an electrical substrate
material is provided which comprises a thermosetting matrix which
includes a polybutadiene or polyisoprene resin and an unsaturated
butadiene or isoprene containing polymer in an amount of 25 to 50
volume percent; a woven glass fabric in an amount of 10 to 40
volume %; a particulate, preferably ceramic, filler in an amount of
from 5 to 60 volume %; a flame retardant; and a peroxide cure
initiator. A preferred composition has 18% woven glass, 41%
particulate filler and 30% thermosetting matrix.
The foregoing component ratios, and particularly the relatively
high range of particulate filler, is an important feature of this
invention in that this filled composite material leads to a prepreg
which has very little tackiness and can therefore be easily handled
by operators. This low tackiness feature allows for the use of
conventional automated layup processing, including foil cladding,
using one or more known roll laminators. While the prepreg of this
invention is tack-free enough to be handled relatively easily by
hand, it is also tacky enough to be tacked to itself using a roll
laminator (e.g., nip roller) at room temperature. In addition,
another important feature of this invention is the low amount of
glass fabric filler relative to the higher range of particulate
filler which leads to improved (lower) CTE in the Z axis or
thickness direction, improved electrical performance (e.g.,
dissipation factor), lower cost and the ability to tailor
dielectric constant through appropriate selection of particulate
fillers.
Still another important feature of this invention is that the cure
temperature for lamination is significantly lower than required by
U.S. Pat. No. 5,223,568 with lamination temperatures typically in
the range of 330 to 425.degree. F. The low temperature cure
conditions allow for the use of bromine containing fire retardant
additives as well as permitting the use of conventional circuit
fabrication (e.g., lamination) equipment. The relatively low
temperature cure is achieved using an appropriate amount of organic
peroxide such as dicumyl peroxide and t-butyl perbenzoate
peroxide.
In accordance with another embodiment of the present invention, an
electrical substrate material is provided which comprises a
thermosetting matrix which includes a single resin, polybutadiene
or polyisoprene resin, in an amount of 25 to 50 volume %; a woven
glass fabric in an amount of 10 to 40 volume %; and a particulate
filler in an amount of from 5 to 60 volume %. A preferred
composition has 18% woven glass, 41% particulate filler and 30%
thermosetting matrix. Preferably, the composition further comprises
a high surface area filler, preferably fumed silica, to reduce
tack; a flame retardant; and a peroxide cure initiator.
The electrical substrate material of this invention includes a
plurality of woven webs (such as E-glass webs) embedded in a
mixture of the polybutadiene or polyisoprene based resin system and
inorganic filler (e.g., silica) laminated between one or two sheets
of conductive foils (e.g., copper) to produce a circuit board
material which is especially well suited for microwave
applications. Of course, if very thin (e.g., less than 3 mil
thickness) cross-sections are desired, then only a single saturated
web may be used for the dielectric.
The above-discussed and other features and advantages of the
present invention will be appreciated and understood by those of
ordinary skill in the art from the following detailed description
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Referring now to the drawings, wherein like elements are numbered
alike in the several FIGURES:
FIG. 1 is a schematic representation of a processing line for the
continuous manufacture of the prepreg in accordance with the
present invention;
FIG. 2 is a cross-sectional elevation view of a circuit substrate
material in accordance with the present invention; and
FIGS. 3-5 are test data depicting the improved (lower) tackiness of
the B-staged circuit substrate in accordance with the polybutadiene
or polyisoprene/unsaturated polymer embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention comprises a thermosetting matrix in the
amount of 25 to 50 volume %, a woven glass fabric in the amount of
10 to 40 volume %, and inorganic particulate filler in the amount
of 5 to 60 volume %. In addition, the present invention includes
one or more organic peroxide initiators in an amount of 1.5 to 6
parts per hundred resin (phr) and a bromine-containing fire
retardant additive in an amount effective to provide fire
retardance.
The resin system, fillers, cross-linking agents, woven web, fire
retardant additives, peroxide initiators, processing conditions and
representative constructions together with Examples will now be
discussed in detail.
Resin System
In one embodiment of the present invention, the resin system used
in the electrical substrate material of this invention is a
thermosetting composition generally comprising (1) a polybutadiene
or polyisoprene resin (or mixture thereof); and (2) an unsaturated
butadiene or isoprene-containing polymer capable of participating
in cross-linking with the polybutadiene or polyisoprene resin
during cure. The polybutadiene or polyisoprene resins may be liquid
or solid at room temperature. Liquid resins may have a molecular
weight greater than 5,000 but preferably have a molecular weight of
less than 5,000 (most preferably between 1,000 or 3,000). The
preferably liquid (at room temperature) resin portion maintains the
viscosity of the composition at a manageable level during
processing. It also crosslinks during cure. Polybutadiene and
polyisoprene resins having at least 90% 1,2 addition by weight are
preferred because they exhibit the greatest crosslink density upon
cure owing to the large number of pendent vinyl groups available
for crosslinking. High crosslink densities are desirable because
the electrical circuit substrates exhibit superior high temperature
properties. A preferred resin is B3000 resin, a low molecular
weight polybutadiene liquid resin having greater than 90 weight %
1,2 addition. B3000 resin is commercially available from Nippon
Soda, Ltd.
The unsaturated polymer preferably comprises a thermoplastic
elastomer and more preferably includes a linear or graft-type block
copolymer that preferably has a polybutadiene or polyisoprene block
with at least 50% by weight, 1,2 addition and a thermoplastic block
that preferably is styrene or .alpha.-methyl styrene. The high
proportion of 1,2-addition in the polyisoprene or polybutadiene
block leads to high crosslink densities after the curing step, as
is the case with the polybutadiene or polyisoprene resin described
above. A preferred copolymer is a styrene-butadiene-styrene
triblock copolymer, e.g., Kraton DX1300 (commercially available
from Shell Chemical Corp.).
The thermoplastic elastomer may also contain a second block
copolymer similar to the first except that the polybutadiene or
polyisoprene block is hydrogenated, thereby forming a polyethylene
block (in the case of polybutadiene) or an ethylene-propylene
copolymer (in the case of polyisoprene). When used in conjunction
with the first copolymer, materials with greater "toughness" can be
produced. Where it is desired to use this second block copolymer, a
preferred material is Kraton GX1855 (commercially available from
Shell Chemical Corp.) which is believed to be a mixture of
styrene-high 1,2 butadiene-styrene block copolymer and
styrene-(ethylene-propylene)-styrene block copolymer. Particularly
preferred compositions are those in which the resin is
polybutadiene, the first block copolymer is
styrene-butadiene-styrene triblock copolymer (m=n=1), and the
second block is styrene-(ethylene-propylene)-styrene triblock
copolymer (m=n=1), the ethylene-propylene block being the
hydrogenated form of an isoprene block.
Thus, in a preferred embodiment, the unsaturated polymer comprises
a solid thermoplastic elastomer block copolymer having the formula
X.sub.m (Y--X).sub.n (linear copolymer) or ##STR1## (graft polymer)
where Y is a polybutadiene or polyisoprene block, X is a
thermoplastic block, and m and n represent the average block
numbers in the copolymer, m being 0 or 1 and n being at least 1.
The composition may further include a second thermoplastic
elastomer block copolymer having the formula W.sub.p --(Z--W).sub.q
(linear copolymer) or ##STR2## (graft copolymer) where Z is a
polyethylene or ethylene-propylene copolymer block, W is a
thermoplastic block, and p and q represent the average block
numbers in the copolymer, p being 0 and 1 and q being at least
1.
Preferably, the polybutadiene or polyisoprene resin and the
polybutadiene or polyisoprene block of the first block copolymer
making up the thermoplastic elastomer have at least 90% by weight
1,2 addition. The volume to volume ratio of the polybutadiene or
polyisoprene to the thermoplastic elastomer preferably is between
1:9 and 9: 1, inclusive.
Other free radical curable polymers which can co-cure with
butadiene polymers may be added (such that 1,2-butadiene polymers
are still the major polymeric ingredient) for specific property or
processing modifications. Such possible modification purposes
include toughness, adherability to copper foil and copper plating,
and prepreg handling characteristics. These co-curable polymers
include random and block copolymers of primarily 1,3-addition
butadiene or isoprene with styrene, alpha-methyl styrene, acrylate
or methacrylate, or acrylonitrile monomers; homopolymers or
copolymers of ethylene, such as polyethylene, ethylene-propylene
copolymer and ethylene-propylene-diene terpolymers,
ethylene-ethylene oxide copolymers; natural rubber; norbornene
polymers such as polydicyclopentadiene; hydrogenated diene polymers
such as hydrogenated styrene-isoprene-styrene copolymers and
butadiene-acrylonitrile copolymers; and others. Levels of these
co-curable polymers should be less than 50% of the total polymeric
component.
In still another preferred embodiment of the present invention, the
resin system comprises only a single resin, i.e., either
polybutadiene or polyisoprene alone, without a second polymeric
component. As with the two-component resin systems, the
polybutadiene or polyisoprene resins may be liquid or solid at room
temperature. Liquid resins may have a molecular weight greater than
5,000 but preferably have a molecular weight of less than 5,000
(most preferably between 1,000 or 3,000). The preferably liquid (at
room temperature) resin portion maintains the viscosity of the
composition at a manageable level during processing.
Polybutadiene and polyisoprene resins having at least 90% 1,2
addition by weight are preferred because they exhibit the greatest
crosslink density upon cure owing to the large number of pendent
vinyl groups available for crosslinking. High crosslink densities
are desirable because the electrical circuit substrates exhibit
superior high temperature properties. A preferred resin is B3000
resin, a low molecular weight polybutadiene liquid resin having
greater than 90 weight % 1,2 addition. B3000 resin is commercially
available from Nippon Soda, Ltd.
Particulate Filler Material
The volume % of the filler (based upon the combined volume of the
resin system, woven fabric and particulate filler) is between 5 and
60%, inclusive and preferably between 30% and 50%. Examples of
preferred fillers include titanium dioxide (rutile and anatase),
barium titanate, strontium titanate, silica (particles and hollow
spheres) including fused amorphous silica and fumed silica;
corundum, wollastonite, aramide fibers (e.g., Kevlar), fiberglass,
Ba.sub.2 Ti.sub.9 O.sub.20, glass spheres, quartz, boron nitride,
aluminum nitride, silicon carbide, beryllia, alumina or magnesia.
They may be used alone or in combination.
In an important and preferred feature of this invention, the
particulate filler is present in an amount which is (1) greater
than the amount (in volume %) of thermosetting composition
(preferably the ratio of filler to thermosetting composition is
45:55) and (2) greater than the amount (in volume %) of the woven
fabric.
Particularly preferred fillers are rutile titanium dioxide and
amorphous silica because these fillers have a high and low
dielectric constant, respectively, thereby permitting a broad range
of dielectric constants combined with a low dissipation factor to
be achieved in the final cured product by adjusting the respective
amounts of the two fillers in the composition. To improve adhesion
between the fillers and resin, coupling agents, e.g., silanes, are
preferably used.
As will be discussed hereinafter, the material described herein is
preferably used as a dielectric substrate in a circuit laminate
wherein a layer of metal is laminated thereto. Preferably, the
filler material and quantity thereof is selected so as to provide
the substrate with a coefficient of thermal expansion which is
equal or substantially equal to the coefficient of thermal
expansion of the metal layer.
With respect to the single resin embodiment of the present
invention, a very high surface area particulate filler such as
fumed silica may be additionally used to prevent tackiness and
stickiness in the prepreg. The preferred fumed silica is available
from Degussa under the trade name AEROSIL 200, and has a surface
area of around 200 m.sup.2 /g, with a typical primary particle size
of 12 nm.
The amount of fumed silica used may be in the range from about 0.2
volume % to about 5 volume percent, and preferably in the range
from about 0.5 volume % to about 1.5 volume %. Thus, the loading
level of such silica may be as low as 1% by weight and still yield
a prepreg with very similar tack characteristics to those found in
the two-component system. Apparently, such very high surface area
silica is much more effective at reducing tack than the standard
sized amorphous silica (10 .mu.m median), as the addition of only
about 1% fumed silica made a large reduction in tack to a prepreg
already containing 66% amorphous silica.
Woven Web
The fiber reinforcement comprises woven, thermally stable webs of a
suitable fiber, preferably glass (E, S, and D glass) or high
temperature polyester fibers (e.g., KODEL from Eastman Kodak). The
web is present in an amount of about 10 to 40 volume %, and
preferably about 15 to 25 volume % with respect to the entire
laminate. Such thermally stable fiber reinforcement provides the
laminate with a means of controlling shrinkage upon cure within the
plane of the laminate. In addition, the use of the woven web
reinforcement renders a dielectric substrate with a relatively high
mechanical strength.
Preferred examples of the woven fiberglass web used in the present
invention are set forth in the following Table:
______________________________________ FIBERGLASS WOVEN WEBS
Manufacturer Style Thickness (in.)
______________________________________ Fiber Glast 519-A 0.0015
Clark-Schwebel 112 0.0032 Clark-Schwebel 1080 0.0025 Burlington 106
0.0015 Burlington 7628 0.0068
______________________________________
Fire Retardant Additive
Preferably, the present invention includes a flame retardant such
as a bromine-containing flame retardant in an amount of 20 to 60
phr. Examples of suitable brominated flame retardants include
Saytex BT 93W (ethylene bistetrabromophthalimide), Saytex 120
(tetradecabromodiphenoxy benzene) or Saytex 102 (decabromo
diphenoxy oxide).
Curing Agent
A curing agent is added to the composition to accelerate the curing
reaction. When the composition is heated, the curing agent
decomposes to form free radicals, which then initiate crosslinking
of the polymeric chains. Preferred curing agents are free radical
cure initiators such as organic peroxides, e.g., dicumyl peroxide,
t-butylperbenzoate and t-butylperoxy hexyne-3, all of which are
commercially available. The peroxide curing agent is provided in an
amount of between 1.5 and 6 phr.
Processing
In general, the two-component thermosetting compositions are
processed as follows. First, the polybutadiene or polyisoprene
resin, thermoplastic elastomer, particulate fillers, curing agents,
flame retardants, and coupling agent (if any) are thoroughly mixed
to form a slurry in conventional mixing equipment. The mixing
temperature is regulated to avoid substantial decomposition of the
curing agent (and thus premature cure). Mixing continues until the
particulate filler is uniformly dispersed throughout the resin. The
particulate filler may be pretreated with coupling agents
(preferably silanes) in a separate step for more efficient use of
the agents.
Next, conventional prepreg manufacturing methods can be employed.
Typically the web is impregnated with the slurry, metered to the
correct thickness, and then the solvent is removed (evaporated) to
form a prepreg.
One processing system useful in making a prepreg in accordance with
the present invention is shown in FIG. 1 and includes (from left to
right) a roll 10 of woven glass web 11 which unwinds through a
first accumulator 12 to a series of drive rolls 14. The web 11 then
passes into the coating area 16 where the web is passed through a
saturation tank 20 (which contains the mixture of polymer,
particulate filler, solvent and other components) and then through
a pair of metering rolls 22. The web 11 thereafter travels the
length of a drying tower 18 for a selected period of time until the
solvent is evaporated from the web whereupon the web passes through
drive rolls 28, a second accumulator 30 and finally web 11 (which
is now a prepreg) is wound onto roll 32.
The lamination process entails a stack-up of one or more prepreg
layers between one or two sheets of conductive foil (copper). This
stack-up is then densified and cured via lamination or a
combination of lamination and oven baking.
The stack-up is cured in a conventional peroxide cure step; typical
cure temperatures are between 330 and 425.degree. F. (165 to
218.degree. C.). In accordance with an important feature of this
invention, unlike U.S. Pat. No. 5,223,568, no additional high
temperature cure step is needed to increase crosslink density. It
will be appreciated that the '568 patent requires a high
temperature cure where the temperature is greater than about
250.degree. C. but less than the decomposition temperature of the
resin (typically about 400.degree. C.).
Referring now to FIG. 2, a cross-sectional view of electrical
substrate material in accordance with the present invention is
shown generally at 40. Electrical substrate 40 has been laminated
in accordance with one of the processes described above wherein a
woven web 42 is impregnated with a resin system/filler composition
44 and laminated between two copper foils 46, 46' to produce a
circuit board laminate. As discussed above with reference to the
processing conditions, the resin system 44 may either be cast onto
woven web 42 using known prepreg manufacturing equipment or web 42
may be saturated by resin system 44 by sandwiching web 42 between a
pair of bond plys formed from resin system 44 and laminating the
stack up together with the copper cladding 46, 46'. While FIG. 2
depicts a single layer of woven web 42, it will be appreciated that
typically a plurality of layers of saturated web 12 will be used in
forming circuit laminates in accordance with the present invention.
However, a single layer as shown in FIG. 2 is desirable where very
thin cross-sections (less than 3 mils) are required.
With respect to the single-resin embodiment according to the
present invention, processing and laminate production was similar
to the methods described above. Thus, the components were mixed
with solvent (xylene), saturated onto 1080 fiberglass, and dried at
room temperature to make prepregs. These prepregs were then stacked
(6 layers), placed between sheets of 1 -oz. ED copper foil and
laminated according to the above procedures. Initially, typical
lamination conditions were used, i.e., heating at 350.degree. F.
for 1.5 hours at 350 psi (Samples 6 and 7). However, the properties
of samples laminated at 350 psi indicated that the samples were not
being fully densified: the specific gravity, dielectric constant,
and copper adhesion were all low. For this reason, samples were
also laminated at 989 psi (Example 8). The resulting laminates
displayed considerably better copper adhesion, as well as more
typical specific gravity and dielectric strength values. The low
dielectric strength and dissipation factor values were still not
optimal, probably due to the tendency of the fumed silica to adsorb
moisture onto its surface. (The manufacturer's literature in fact
states that up to 1.5% by weight of the silica could be water.)
Either a pre-drying or surface treatment step using silane or other
hydrophobic coating may be employed to resolve these problems. Any
silane or other hydrophobic coating would need to be compatible
with the resin system of the present invention.
EXAMPLES
The following non-limiting examples further describe the electrical
substrate material of the present invention.
A. Tackiness
In an effort to quantify the tackiness of the prepreg of this
invention, a peel test was developed and applied to a number of
samples.
Test Description
Attempting to simulate a 90.degree. peel test, an Instron (Model
1125) was used to peel apart 2 layers of prepreg. The individual
layers of prepreg were 1" wide and 12" long and were stuck together
by rolling a 10 lb roller over them in the lengthwise direction. A
50 lb tensile load cell was used in conjunction with a 15
inches/minute crosshead speed to measure the peel force or tack.
For verification of the data, the tests were duplicated using a 10
lb cell and 12 ipm.
Test Samples
Four prepreg formulations were created for this test as shown in
the table below. Using only 106 style fiberglass, prepregs were
made in which the particulate filler, resin and rubber contents
varied.
______________________________________ Prepreg Component, % by
volume Resin Rubber Woven Sample No. Filler (PBD) (SBS) Glass Other
______________________________________ 2075-62-1 25 32 20 18 5
2075-62-2 34 26 16 18 6 2075-62-3 25 41 11 18 5 2075-62-5 34 34 9
18 5 ______________________________________
Results
The measured peel values range from 0 to 0.35 pli. FIG. 3 plots the
tack versus SBS (rubber) content for the two filler loadings used.
From this plot, the resulting tack is more sensitive to rubber
content at the lower filler loading. Alternatively, FIG. 4 plots
the tack versus filler content. In this case, the resulting tack is
more sensitive to filler content at the lower rubber loading. FIGS.
3 and 4 lead to the conclusion that the combination of filler and
rubber volumes effect tack. If one looks at the resulting resin
contents versus tack (FIG. 5), there is a good correlation between
resin volume present and tack. Put simply, it appears that an
important factor for tackiness is the amount of resin present and
to reduce tack it does not matter whether the resin is displaced by
filler or rubber so long as the resin is displaced.
B. Two-Component Polybutadiene/Polyisoprene Example
Formulations
The following five examples show representative electrical, thermal
and mechanical data for the two-component laminates of the present
invention. In accordance with an important feature of this
invention, the dissipation factor of the resultant laminate is less
than or equal to 0.007, which renders this material well suited for
use in microwave applications.
Example 1
This is a preferred embodiment. The laminate consisted of five
layers of prepreg for a total dielectric thickness of 0.023 inches
(") Note the high filler and low rubber contents.
Example 2
This sample contained a particulate filler loading lower than the
preferred embodiment but had a higher rubber content. The laminate
was made with five layers of 1080 woven glass resulting in a
dielectric thickness of 0.021".
Example 3
This sample contained titania (TiO.sub.2) particulate filler
compared to the silica (SiO.sub.2) found in the other examples. The
laminate contained 10 layers of 1080 woven glass resulting in a
dielectric thickness of 0.028".
Example 4
This laminate had the rubber replaced in the formulation with more
resin. The laminate's construction utilized four layers of 1080
woven glass and resulted in a dielectric thickness of 0.016".
Example 5
This sample contained more rubber than resin. The resulting
laminate was 0.020" thick and utilized five layers of 1080 woven
glass.
______________________________________ Component, Source Sample No.
(% by total weight) 1 2 3 4 5
______________________________________ Formulations, Examples 1-5
B3000 Resin, Nippon 14.6 13.5 12 21.2 4.4 Soda D1300 (Kraton)
Rubber, 3.8 9.3 3 0 13.1 Shell FB-35 Fused Silica, 0 44.7 0 0 51.3
Denka Minsil 5 Fused Silica, 51 0 0 45.7 0 Minco Ticon HG Titania,
TAM 0 0 53.2 0 0 Woven Glass, 25 26 27 26 25 Clark-Schwebel Silane
0.5 0.4 0.6 0.4 0.5 Brominated Flame 4.5 4.6 3.7 5.3 4.4 Retardant
Catalyst (peroxide) 0.6 1.5 0.5 1.4 1.3 Properties, Examples 1-5
Dielectric Constant* 3.47 3.35 9.54 3.22 3.42 Dissipation Factor**
0.0035 0.0042 0.0059 0.0053 0.0035 Specific Gravity (g/cc) 1.83
1.75 2.47 1.76 1.83 Copper Bond (pli) 4.4 5 2.1 3.2 3.7 Water
Absorption (% wt) N/A 0.09 N/A N/A 0.67
______________________________________ *Dielectric constant (Dk)
values are the averages of the measured Dk's from a 1-10 Ghz
frequency sweep. **Dissipation Factor (Df) values are the lowest
recorded value of a given 1-10 Ghz frequency sweep. Specific
gravity test method: ASTM D79291 Copper bond: IPCTM-650 2.4.8 Water
absorption IPCTM-650 2.6.2.1 (with 48 hr exp.)
In general, the preferred formulations of the present invention
minimize fiber content and maximize particulate filler content.
This high particulate filler content (preferred ratio of resin to
filler is 45:55) leads to improved (lower) CTE in the Z-axis
direction, improved electrical performance, lower cost and other
features and advantages. While the prior art discussed above
generally discloses filled polybutadiene laminates and laminates
based on other resin systems which employ fiber and particulate
fillers, no prior art to which Applicants are aware utilize the
combination of:
1. thermosetting matrix comprised of polybutadiene or polyisoprene
resin and an unsaturated butadiene or isoprene containing polymer
in an amount of 25 to 50 volume %
2. woven fabric reinforcement in an amount from 10 to 40 volume %;
and
3. particulate filler in an amount of 5 to 60 volume %.
In general, the present invention utilizes a higher particulate
filler level and a lower woven fabric level. Preferably, the use in
the thermosetting composition of a high molecular weight copolymer
permits the use of these higher levels of particulate fillers, all
of which leads to improved rheological control, reduced tack and
reduced shrinkage. More particularly, the combination of an
extremely high loading level of particulate filler, woven glass and
an unsaturated polymer while still being processable using standard
industry equipment represents an important advance in the circuit
materials field. In addition, the unexpected result that the
particulate filler can be used to eliminate tackiness of the liquid
polybutadiene resin represents still another important feature of
this invention
C. Single Resin Polybutadiene/Polyisoprene Formulations
The following examples show representative electrical, thermal, and
mechanical data on the preferred single resin embodiment of the
laminate of the present invention, wherein only a single resin
system comprising a polybutadiene or a polyisoprene resin is used.
The entire SBS rubber portion of the formulation is replaced on a
weight basis with additional liquid resin.
Example 6
The final laminate properties of this example, where the
unsaturated rubber component is replaced by liquid resin on a
weight basis, are very similar to those of the two-component
system. The key differences are a loss of flexural strength and an
increase in flexural modulus, as well as an increase in xylene
absorption. Since the unsaturated rubber component can act as a
toughening agent, the changes in flexural properties are expected.
However, direct replacement of the unsaturated rubber component
with additional liquid resin resulted in very tacky, sticky
prepregs. This level of tack can pose handling problems in some
applications.
Example 7
In this Example, very high surface area fumed silica has been added
to the composition, thereby eliminating tack and stickiness in the
prepreg. Lamination was performed at 350 psi. Except for
dissipation factor and dielectric strength, the resulting materials
have very similar properties to those observed in the
above-described two-component system. Additional treatment of the
fumed silica may improve these properties.
Example 8.
In this Example, lamination of a single resin system containing
fumed silica was laminated at 989 psi.
Example 9.
Example 9 is a representative two-component resin system according
to the invention described above, comprising a polybutadiene or
polyisoprene resin and an unsaturated polymer, included for
comparison purposes.
______________________________________ Component, Source Sample No.
(% by total weight) 6 7 8 9 ______________________________________
Formulations, Examples 6-9 B3000 Resin, Nippon Soda 16.9 16.7 16.7
12.6 CE44I Amorphous Silica, CE 49.5 49 49 46.2 Minerals Aerosil
200 Fumed Silica, Degussa -- 0.7 0.7 -- A174 Silane, OSI 0.5 0.5
0.5 0.4 Luperox 500R Catalyst, Elf 0.7 0.7 0.7 0.6 Atochem BT-93W
Flame Retardant, 7.4 7.4 7.4 7.0 Albemarle 850BD (Vector) Rubber,
Dexco -- -- -- 3.2 Woven Glass, Clark-Schwebel 25 25 25 30
Properties, Examples 6-9 Lamination Pressure (psi) 350 350 989 350
Thickness (mils) 23.4 23 24 20 Copper Bond (pli) 5.0 3.0 4.8 5.4 %
Bow (after etch on one side) 7.2 7.1 5.6 6.0 % Twist (after etch on
one side) 6.3 6.3 6.9 5.0 Dielectric Strength (V/mil) 783 688 631
800+ Specific Gravity (g/cc) 1.89 1.79 1.86 1.86 MD Flexural
Strength (Kpsi) 27.2 28.3 31.3 33.5 CMD Flexural Modulus (Kpsi)
23.8 21.6 26.3 28.0 Dielectric Constant* 3.40 3.25 3.46 3.45
Dissipation Factor** 0.0041 0.0045 0.0055 0.0040 Xylene Absorption
(% wt) 2.55 1.98 1.87 1.60 ______________________________________
*Dielectric constant (Dk) values are the averages of the measured
Dk's from a 1-10 Ghz frequency sweep. **Dissipation Factor (Df)
values are the lowest recorded value of a given 1-10 Ghz frequency
sweep. *Specific gravity test method: ASTM D79291 Copper bond:
IPCTM-650 2.4.8 Xylene absorption IPCTM-650 2.6.2.1 (with 48 hr
exposure)
The above Examples 6-9 demonstrate that a single resin composition
according to the present invention can be used to form circuit
board laminates with desirable properties. With the addition of a
small amount of a high surface area particulate, preferably fumed
silica, the composition is readily workable for manual and
automated handling, and thus economical to prepare.
While preferred embodiments have been shown and described, various
modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustrations and not limitation.
* * * * *